Loudspeaker horns of the general type disclosed here are designed to provide an acoustical output of constant directivity and beamwidth as a function of frequency and to provide a constant acoustic load to the driver. However, it is well recognized that a horn can only offer directivity control down to frequencies at which the wavelength is comparable to horn mouth size. In addition, maintaining directivity control at higher frequencies has also proven difficult with many prior art designs due to narrowing at the midrange and high frequencies, polar lobing, or other deficiencies.
An early horn design is the conical horn, such as found on the early phonographs or victrolas. However, the conical horn exhibited poor low-frequency response as well as midrange narrowing and other deficiencies. Another well known loudspeaker horn design is the radial-sectoral horn, which also exhibited midrange narrowing of beamwidth and polar lobing, although somewhat better low frequency performance was provided. Another well known horn design is shown in U.S. Pat. No. 2,537,141, which discloses a multi-cellular radial sectoral horn. This design also suffered from the deficiencies noted above.
Another loudspeaker horn design is shown in U.S. Pat. No. 4,071,112, by the present inventor. The horn disclosed in the '112 patent employs a throat section having an exponentially increasing area coupled to a mouth section having an area which increases conically. By providing additional flaring at the mouth, the problem of midrange narrowing was lessened; thus, beamwidth (the included angle between the -6 db points in a polar plot) is improved. However, other characteristics of the horn could still be improved.
Still another attempt to design the ideal horn is shown in U.S. Pat. No. 4,187,926, which uses substantially the same approach as found in U.S. Pat. No. 4,071,112. The design disclosed by the '926 patent involves the use of a first pair of sidewalls extending from the driver to the mouth at a predetermined angle, and another pair of sidewalls which are parallel at the throat and then flare to form a bell section at a second fixed angle. The two pairs of sidewalls are joined at the mouth of the horn. This design also suffers from poor low frequency response and nonuniform sound dispersion at some frequencies.
The present invention overcomes or improves upon many of the limitations encountered with the prior loudspeaker horn designs discussed above. In accordance with the present invention, a horn is comprised of a pair of vertical sidewalls and a pair of horizontal sidewalls disposed at right angles to one another, one of which is defined by a surface of revolution. The curvature of the surface of revolution, and the contour of the remaining pair of sidewalls, is defined by a power series formula which includes factors determined by the desired dispersion angle, low frequency limit, throat diameter, and rate of flare. Because the vertical dispersion angle and other characteristics may differ from the horizontal characteristics, the curvature of the vertical sidewalls is separately defined from the horizontal sidewalls.
Once the above characteristics are selected, other dimensions of the loudspeaker horn are computed. Thus the horn throat included angle, horn length, and horn mouth width are calculated and used to provide the factors for the power series formula described above. The process is repeated for the second pair of sidewalls, using the geometrics and factors which are appropriate for the desired dispersion angle in the second plane. The two pairs of sidewalls are then joined congruently at the mouth and the gap formed by one of the pairs of sidewalls is connected to the throat of the horn by means of a connecting section.
It is therefore one object of the present invention to provide an improved loudspeaker horn.
It is another object of the present invention to provide a loudspeaker horn having directional characteristics which are substantially constant with frequency.